1. Field of the Invention
The invention is for use in conjunction with film to video transfer machines, with its particular application utilizing signal processing techniques to produce a video image from the film of higher quality than would be the case without use of the invention.
2. Brief Description of the Prior Art
In film to video transfer machines such as the telecine machines sold by Rank Cintel, film containing a moving video image is run through a light/lens/scanner system and each film frame is sampled and video signals are generated suitable for recording on a video tape. In sampling systems of this type, it is well-known that aliasing will occur if the signal being sampled has energy above a frequency which is one half the sampling frequency. A frequency one half the sampling frequency is known as the Nyquist frequency. In film to video transfer machines, it is common practice to use a non-interlaced raster scanned CRT to convert the photographic film images to video signals. The light from the CRT is focused on the film and photo detectors on the other side of the film produce electrical signals representing the color and intensity of the film images as they pass by the photo detectors.
In film to video transfer machines, it is also standard practice to convert the video signals recovered from the film to digital signals. The digitized image is then stored in a memory device to provide for sequential to interlace conversion. The memory device is called a frame store and it also does the translation from the film frame rate to the video output rate. For example, the film rate could be 23.98 frames per second and the output video standard rate could be 29.97 frames per second.
The video signals are passed through anti-aliasing low pass filters before being converted to digital signals. There is normally no filtering vertically. Vertical filtering is difficult to perform optically because the distance between scan lines changes depending on zoom amount and film velocity. It is also not desirable reduce the horizontal resolution. The scanning spot could be expanded vertically, but this will result in less resolution and may be difficult to perform when electronic rotate is used. Images that have high frequency components will cause vertical aliasing.
Another effect that is objectionable is interlace flicker. This occurs when adjacent line are significantly different. Every other line comes from a different field at half the frame rate. This effect can be noticed for example when the image contains horizontal lines such as a car grill or horizontal window blinds. Another noticeable effect is that diagonal lines tend to be jagged.